Directional power relay control means



Dec. 1o, 1935. R. L WARD l 2,023,653

DIRECTIONAL POWER RELAY CONTROL MEANS Dec. 10, 1935. R, l, WARD 2,023,653

DIRECTIONAL POWER RELAY CONTROL MEANS Filed Sept. 14, 1934 2 Sheets-Sheet 2 Patented Dec. 10, 1935 DIREOTIONAL POWER RELAY I g CONTROL MEANS Robert I. Ward, Chicago, Ill.

Application September 14, 1934, Serial No. 743,979

12 Claims. (Cl. 175-2'94) This invention is a modification and continuation of my co-pending application, Serial No. 573,754, filed November 9, 1931, and relates to reverse power differential protection means for use in alternating current circuits, being more particularly directed to the use of a thermionic tube control for delaying the action of the protection means.

' In the protection system disclosed in my abovementioned application, I provide a directional relay'in the form of a thermionic tube wherein a certain alternating current Voltage is applied to the grid of the tube, a certain alternating currentis applied to the plate ofthe tube, and the plate circuit serves as an indication of variations in the relative phase angle between the grid and plate voltages. The two applied voltages may be functions of the line voltage and current, in which case the relay indicates the direction of power flow, or may be functions of the currents flowing in different portions of the line, in which case the relay is used for differential line protection, or for overload conditions, or for protection against such faults as result in a relative phase change in the voltages or currents in different parts of the alternating current circuit. The grid and plate circuits are so disposed with relation to 'each other that the grid prevents any substantial current flow in the plate circuit when the phase angle between the line current and line voltage is such as to indicate normal power flow in one direction in the line, and permits current to ow in the plate circuit when the phase angle has changed to indicate a change in direction of power flow, an overload condition, or the like.' A

The plate circuit is connected to the energizing coil of a relay which controls the circuit leading. to the trip coil of a circuit breaker or other interrupting means, and upon predetermined flow of current in the plate circuit the relay is actuated to close this circuit for interrupting the line. disclosed in my copending application, mechanical time delay means are provided for controlling the operation of this relay.

The present invention, in its preferred embodiment, contemplates the provision of a thermionic directional power relay with time-current characteristics similar to thosefof a standard reverse power relay, the time-current characteristics corresponding in operation tothe operation of the ordinary type of mechanical time-controlled relay but being obtained independently of the movement of mechanical parts.

A primary object of the present invention is the provision ofa thermionic directional or overload power relay circuit for an alternating current line having a time-controlled thermionic tube for delaying the action of the tripping relay, the time delay being selectively controlled independently of the movement of mechanical parts and capable 5 -of extremely sensitive adjustment.

Another object of the present invention is to provide a thermionic tube in the time delay circuit of the tripping relaywhich has a grid normally subjected to a predetermined potential 10 negative with respect to the cathode of the tube. The potential impressedy upon this tube is balanced at such a point as to maintain substantially no current ow through the plate circuit of this tube. 'Ihe directional or Overload thermionic power re- 15 lay is adapted, upon a variation in phase angle such as heretofore explained, to impress a positive potential upon the/grid of the time delay controlling tube, and thus counteracts the negative voltage of the biasing circuit. Upon a pro- 20 portiona'te increase in the impressed positive potential supplied by the power relay circuit, the grid circuit of the tube begins to allow current iiow through the plate circuit, resulting in ener- A still further Object of the present invention is. the provision of adjustable means for selectively varying the time period necessary before, the effect of the negative biasing circuit is sulficiently counteracted to permit current flow 30 through the plate circuit.

An additional feature of the present invention is the provision of a timing circuit which is independent of the directional control circuit controlled by the thermoitic directional power relay, and which is not energized until the reverse current flow exceeds a predetermined minimum. The timing circuit is therefore independent of thegrid voltage in the directional power relay and also independent of current flow in the plate 40 circuit of the power relay below the predetermined minimum current ow necessary to energize the .timing circuit.v

It is also an object of the present invention to couple both the main thermionic directional power relay, and the thermionic time control relay to a life indicator circuit, whereby deterioration of the thermionic tubes, due to lower electron emission of the cathode, or loss of vacuum in the tube, will be indicated prior to actual deterioration of the tube, so that the tube may be replaced before' its usefulness is destroyed. h

It is another object of the invention to provide a timing circuit having such characteristics that it will not be affected by surges on the Iline orV temporary power disturbances if the power is flowing in the normal direction, and will not actuate the tripping circuit under these conditions.

An additional advantage secured by the present invention is the provision of a timing circuitI in which the operating time starts after the reversal of power flow in the main transmission line.

Compared with the initial cost and maintenance of the standard reverse power relays, the thermionic time controlled relay is distinctly advantageous, and has no moving parts except the simple auxiliary type relays.

An additional feature secured by the use of such a thermionic time control circuit is that it is more sensitive under low voltage conditions than the present type of reverse power relays, and thus more adjustable in its operation to provide a control capable of meeting extremely exacting requirements.

Other objects and advantages of the present invention will appear more fully from the following detailed description, which, taken in connection with the accompanying drawings, will disclose to those skilled in the art the particular construction and operation of a preferred embodiment of my invention.

In the drawings: Y

Figure l is a circuit diagram of one form of my directional power relay control means provided with the thermionic control timing circuit;

Figure 2 is a slightly modified circuit diagram of a control means embodying the present invention; and

' Figure 3 is a diagrammatic circuit disclosing the application of one form of my directional power relay control means and timing circuit to a three-phase alternating current transmission line.

Referring now in detail to Figure 1, I have disclosed the station bus 5, which is connected to the alternating current line 6 through a circuit breaker 'i having trip mechanism 8 controlled by the trip coil 9.

The line 6 is provided with a line current transformer II) of the standard type, and has special saturating transformers as shown at I2, connected on one side to the suppressor grid I3`in the thermionic reverse power relay control tube I4, and also through the conductor 39 to the cathode of the tube. The opposite side of the saturating current.transformer I2 is, for expedience, connected to a resistance II interposed between the positive bus I5 and negative bus I 6 of a directcurrent operating bus supply circuit, the negative bus I6 being connected through conductor I1 to the energizing coil 9, which has its circuit completed through the conductor I8, contact I9, relay 20, contact 22 and conductor leading to the positive bus I5. The relay 20 is adapted to be energized by the coil 23 connected by conductor 24 to the bus I5, and also connected to the plate 25 of the thermionic time control tube 26 by means of conductor 21.

The station bus 5 is provided with a potential transformer 28, the secondary of this transformer 29 having a filament winding 30, the secondary of the filament winding 30 leading to the heating filaments 32 and 33 ofthe tubes I4 and 2B, respectively. The cathode 34 of the tube I4 is connected to the potential transformer 28 and, if desired, may be connected to ground at this transformer. From the secondary 29 of the potential transformer a conductor leads to the grid 35 controlling the flow of electrons from the cathode 34 to the plate 33 connected to the secondary of the current transformer. A suitable fixed resistance or lamp 35 is interposed in this circuit to provide a fixed potential upon the grid 35.

It will be noted that normally the transformer I2 is connected through resistor 31 to a conductor 3I which is at zero potential with respect to the tube 2S. The current flow through resistor 31 thus is controlled by the circuit extending through the plate of the tube I4.

As is normally the case in a control system of this type, as described in detail in my above referred to copending application, the grid 35 normally prevents electron flow from the cathode 34 to the plate 38, there being a certain current impressed upon the plate 38 which is in such phase relationship that the current in the plate circuit controlled by the plate 38 is maintained either at substantially zero, or at a substantially xed predetermined minimum value.

Referring now to the timing circuit for the control system shown in Figure l, the resistor tap 40 is adjustably connected to the resistor 31, so that any desired minimum ampere setting may be obtained, depending upon the sensitivity and time-current characteristics desired in the circuit. The tap 4E) is connected through conductor 42 to the resistor or grid leak 43, which, in turn, is connected to the grid 45 of the tube 25. However, the grid 45 is also connected, through resistor 44 and conductor 45, to the negative bus I6. During normal operation of the station bus 5 and the line 5, the negative operating bus i6 supplies a negative potential through conductor 4S and refrom the cathode 34 to the plate 33, thereby al- 4 lowing flow from the saturating type special transformer I2 through the resistor' 31 and plate 38 to the cathode 34. The potential across resistor 31 is transferred, by means of the tap 43, to the conductor 42, and, through resistor 43, is irnpressed upon the grid 45.

The increasing positive potential impressed upon the grid 45 in this manner serves to counteract the negative potential provided by the bus I6 and conductor 46, and thereby overcomes the negative potential on the grid 45. The rate at which the positive potential is increased above the negative potential, which may be of any predetermined value, is controlled by the condenser or capacitor 48, which is connected between the filament winding for the filament 33 and the grid 45. Suitable taps 49 are provided in the condenser 48 for determining the charging rate of the condenser or capacitor. The capacitance of the condenser, being adjustable, serves to adjust the time periodwithin which the positive potential upon the grid 45 is increased to an extent such as to allow current flow from the bus through conductors 24, energizing coil 23, conductor 21 and plate 25 to filament 33, producing suilicient current iiow after a predetermined period of time to effect energization of coil 23 for actuating the relay 20.

The relay 29, upon actuation, bridges between contacts I9 and 22, closing the circuit to the tripping coil 9 for the circuit-breaker or other circuit interrupting means, thus opening the circuit in line 6. It is to be understood that the system is capable of ready application to a threephase alternating current transmission or power line.

Thus, upon a reversal of current flow in the line 6, as sensed by the transformer I2, plate current flows from the plate 38 to the cathode 34, resulting in current flow through the resistor 31 of such value as to provide for impressing a positive potential, that is, with respect to the negative potential imposed by negative bus |6, upon the grid 45 of the thermionic time control tube 26.

I mum current setting of the tap 40, results in actuation of the tripping relay,

applicable for power control means wherein the station bus 5 may operate at low voltage due to a fault condition, or Where the line 6 is not of sufcient length to provide a high reactance. That is, the control circuit is not operable in situations which require close selectivity, and in short operating lines adjacent the station. 'I'his is due to the fact that with a decrease in the bus voltage in station bus 5, there is a corresponding decrease in potential of the grid 35, and instead of speeding up the operation of the tripping relay 20,. the operation is correspondingly slowed down, due to the fact that current flow in the plate circuit controlled by plate 38 is not increased because of the decrease in potential in the grid 35.

'Ihe grid 3 acts to prevent the secondary electrons from the plate 38 returning to the cathode 34, while the screen grid 36, which is connected to the transformer I2 serves, in effect, to reduce the space which the electrons from cathode 34 have to travel to reach the plate 38, and thereby acts as a booster grid. The tube 26 may, if desired, be provided with a cathode, the cathode in that case being connected directly 'to conductor 3|.

The circuit shown in Figure 1 is also subject to the disadvantage that some current will also be flowing in the special transformer I2 during operation of the vline 6, and this current maybe carried through the conductor 42 to the grid 45, thereby not providing as sensitive or selective time control for the circuit as is desirable in certain instances.

- linesV are vof sufficient length to provide a high reactance to prevent large variations in bus voltage due tofault conditions, although the circuit in Figure 1 is considerably'more economical than the hereinafter described circuits, I have provided thetirneycontrol circuit shown generally in Figure 3.1--

In this circuit, I have preferably illustrated the application of the modified control circuit to a three-phase, system, comprising the three station bus conductors |00, |02, and |03, corresponding to the first, second and third phases of a three-phase circuit, and which are connected,

through circuit breaker |04, to the corresponding*- .l lment of the invention, the tube is satisfactory for operation on low plate voltage.

line conductors |05, |06, and |01.

The circuitbreakr |04 has tripping energizingor tripping coil, connected through conductors H0 and-|12 to the negative operating l metti! nism indicated' at |08, whichis lactuated by the.

bus conductor I3 and the positive operating bus conductor |4, respectively, which have resistances thereacross.

Each of the station buses |00, |02, and |03 is provided with a potential transformer indicated 5 generally at I5, and each of the line conductors |05, |06, and |01 is provided with current transformers H6, corresponding to the current transformers ,I0 and l0' of Figures 1 and 2. The potential transformers are preferably connected in certain predetermined phase relationship with respect to the current transformers, to compensate for phase shifting of the saturating transformers and phase shifting introduced by faults on the line. l5 rI'he trippingcircuit for the. circuit breaker trip coil |08 corresponds in detail with the circuit escribed in connection with the embodiments of Figures 1 and 2, distinguishing therefrom only in being provided with three parallellyv connected sets of contacts II1, H0, and .l |9, corresponding to the three phases for the three phase alternating current line. These contacts are each adapted to be actuated by a relay |20 controlled by the energizing coil |2| connected between the 25 positive voperating bus ||4 and the plate |22 of 4"of the tubes |23. The directional power control thermionic relay includes the tubes |30, corresponding to the tube I4 of the circuit disclosed 35 in Figure 1, and the filaments |32 of each of these tubes are also connected to the filament transformer |25.r

The tubes are of special construction, having a plate |33, three grids |34, |35, and |36, 40 and a special plate |31. In addition, the tubes |30 may be provided with an additional plate for connecting the tubes to a tube life indicating circuit, as will be described in connection with Figure 2. The cathodes of the tubes |30 are con- 45 nected to the potential transformers II5, and the grids |36 of the tubes |30 are adapted to control the flow of electrons from the cathodes of the tubes to the plates |33, for controlling the flow of current through the saturating transformers |52 and plates |33. 'I'he grids |34 of the tubes |30 serve to prevent secondary electron discharges from the plates |33 affecting the operation of the control grids, and the grids |35 act as booster grids for decreasing the effective 55 space within the tube through which the electrons from the cathodes must travel to the plates.

This tube has been chosen as vof the particular type shown becausethe plate current in such a tube tends to become constant with increasing of Vthe plate voltage,` and 'this provides for better control for reverse power application. l

The tubes |23 are also of special type, corresponding somewhat to a three-element tube and the characteristics of this tube are such that the plate current increases rapidly with an increase of grid voltage. 'I'his characteristic makes the tube more eicient for use with auxiliary relays, and also, since the plate resistance of the tube is approximately 800 ohms, in a preferred embodi- If desired special plates may be provided for each of the tubes |23 and |30 to connect the tubes to the tube life. indicating circuit.

The transformers |52 of the embodiment shown in Figure 3 are provided with an additional winding |40 added to the special saturating transformer, the winding |40 being employed to supply the positive grid potential to the tube |23, this potential being supplied through conductor |42, connected to the grid |43 of the tube |23 and leading to the resistor |44 connected to one side of the special winding. Thus, when. an abnormal condition results in current ow through plate |31 of the tube |23, the voltage drop across the resistor |48 is such as to produce a positive direct current potential from the common connection between windings |52 and |40 through the cathode |30 and plate |31 to the conductor leading to the other side of winding |40. 'I'he voltage drop across resistor |48 in this circuit provides for a positive potential being impressed through contacts |49, resistor |44 and conductor |42 upon the' grid |43 of the tube |23.

During normal operation of the system, negative potential is impressed 'upon the grids |43 of the tubes |23 by reason of the conductors |46 leading through resistances |41 to the grids |43 from the negative operating bus connection ||3.

lThe resistors |48, connected between the special windings |40 of the saturating transformers |52 and the plates 31, correspond generally to the resistors 31 and 31 of the embodiments disclosed in Figures 1 and 2. This resistance is used in a special plate circuit |31 of the tubes |30, and the special plates |31 of each of the tubes |30 are xed plates surrounding the common cathodes of the tubes, and independent of the other elements of the tubes. The purpose of these elements is to rectify the current from the special windings |40 of the special current transformers to furnish a positive direct current voltage to the tubes |23 when thev contacts |49 of a relay |50 are closed by current flowing through the winding |52 of the special saturating transformer. This current flow is produced by the relative phase displacement between the line current, as indicated by the voltage drop across windings |52 and impressed upon the plate 33,' and the bus voltage impressed upon the grid |36, whereby the grid allows plate current to flow to the cathode of the tube. This ow of current results in energizing the coil |53, actuating the relay |50 -to close the contacts |49, and thereby closing the direct current circuit to the grids of the time control tubes |23.

Inasmuch as the contacts of the auxiliary relay |50 must close before the positive direct current circuit to the grids of the timing circuit is energized, it. will be apparent that the timing circuit cannot initiate its operation until there is a reversalof power suicient to operate the auxiliary relay |50, or a sufcient overload upon the line in the reverse direction to accomplish this purpose. If the fault current of the line is in the reverse direction and is of suflicient magnitude and exists for a suicient period of time, to provide for imposing a predetermined positive potential upon grid |43, current will flow through the plate circuit of tube |23, and the auxiliary relay |20 of the timing circuit then closes its contacts and causes the line circuit breaker toppen in the manner described in connection with", the previous embodiment.

Thus, during normal operation of the protection system, when the relay |50 is unenergized and current is flowing normally in one direction or beyond line conductors |05, |06 and |01, there is not suthcient ow of current caused by an abaoeacte normal line condition to energize theplate circuit through the plates |33 of the tubes |30, and hence no substantial flow ofcurrent sufficient to energize coils |53 of the relays |50. At the same time,

since the relays are opened, there is no direct 5 current voltage imposed upon theresistors or grid leaks |44 from the special orv additional windings |40 of the special saturating transformers |52, and hence there is no'positive potential being applied to the conductors |42. During this 10 time, the grids |43 of the tubes |23 are vunder a negative potential determined by the potential of the operating bus H3, and the resistors |41. This negative potential is sufticient to prevent any substantial current flow in the plate circuit 15 l of tube |23 from the positive bus conductor ||4 through the energizing vcoil |2| of relay |20 and thence through the plates |22 of tubes |23 to ground or to the negative bus. Thus, the relays |20 remain unenergized, and -the grids |43 remain 20 at a constant or predetermined negative potential.

Upon reversal of current flowin the line conductors |05, |05 or |01, of sufficient magnitude and for a suicient period of time to indicate a 25' fault or the like, the special saturating transformers"|52, which are supplying voltage from the current transformers ||6 through the coils |53 of relays |50 to the plate |33, complete a circuit by reason of the grid |36 getting into a 30 relative phase position with respect to the plate |33, and thereby allowing current flow from the plates |33 of the tubes |30 through the cathodes of the tubes, thus completing'a circuit between. coil |53, plate |33 andthe cathode of tube |30. 35 This results in passing an energizing current through the coils |53, resulting. in actuation of relays |50 to close'contacts |49.. IClosing of the contacts |49, therefore, does not occur until a reversal of power has occurred which is of sui- 40 cient magnitude to operate the relay |50.-

The time control circuit therefore begins its eifective control of the tubes |23 only'after this reversal has occurred Aand the relays 50 have been energized. The common conductor of windings |52 and |40 is connected to the cathode of the tube |30, and the plate I3]- completes a circuit through the tube |30 to the other side of the wind--y ing |40. By reason of the special -plates |31, which acts as a rectifier providing a direct current component in resistors |48, a direct current is supplied .from the special windings |40 through the contacts |49 to the resistors or grid leaks |44, which direct current is positive in potential, and this positive potential is applied through the con- 55 ductors |42 to the grids |43 of the tubes |23,' thereby tending to counteract the negative potential supplied by the negative operating bus 3. This produces current ow through the plates |22 of the plate circuits controlling the re- 60 lays |20, and, when a suicient current has been built up in thiscircuit, the relays |20 are ener-` gized to actuate or close the circuit for the tripping coil |09 of the circuit breaker |04.

Preferably the condensers |60, corresponding to the condensers 48 and 48 of Figures 1 and 2, are connected in such manner as to control directly the time required to build up a suiicient positive potential upon the grid |43 to counteract the negative potential impressed thereon by the negative operating buses. The condensers or capacitors |60 are provided with a plurality of taps |62, which provide for selective control of the time-current characteristics of the tubes |23, so that by varying the charging rate of capacitance of the condensers or capacitors, the time necessary for producing operation of the relay |20 after the relay |50 has been energized can be preselected. Also, by varying the minimum current setting for the additional windings |40, or the resistors |44, the time characteristics of the positive potential applied to the grids |43 may also be controlled.

Thus it is apparent that I provide, in the embodiment in Figure 3, an additional winding in the saturatingI transformer which provides for producing a positive direct current potential upon the grid of the time-controlling tubes, this positive potential being effected by means of a special rectifying plate in the circuit of the directional power relay. Further, I provide a system in which the timing circuit is entirely independent of the operating circuit for the directional power control relays, and is actuated only after energization of and independently of the current flowing in the thermionic directional power relay circuit.

Also, because of the characteristics inherent in the timing circuit as disclosed, the relays |20 will not be affected by surges upon the line, or temporary disturbances if the power is owing in the normal direction, due to the time-current characteristics of this circuit as determined by the capacitance of the condensers and the minimum current settings of the direct current positive potential supplying means.

The circuit shown in Figure 2 comprises the current transformer |0' having its primary connected to the line 6, and having its secondary provided with an energizing coil 52 for actuating a relay 53 to engage the spaced contacts 54. The coil 52 is so arranged with respect to the transformer |0' that a predetermined minimum current flow through the secondary of this transformer is necessary in order to produce actuation` of the relay 53. The transformer |2 is connected through the resistor 31 to the biasing cathode 55 of the tube 26' and from there to the conductor 51, which conductor is connected between the negative operating bus |6 and the positive operating bus |5 by means of a resistance such that the potential is maintained substantially zero with respect to the tube 26'. The resistor 31 has a branch connection through conductor 58 to the plate 38' of the tube I4. The tube |4 is employed for rectifying the current in the plate circuit to supply direct current potential to the timing circuit.

The laments 32' and 33' of the tubes |4' and 26', respectively, are connected to the filament heating coils of the larnent transformer 30' in the same manner as noted in connection with Figure 1. When the plate circuitcontrolled by the plate 38 is energized, plate current ows from the transformer I2 through the resistor 31' and conductor 50 to the plate 38', and from the plate to the cathode of the tube I4'. The rectifying tube |4' thus produces directcurrent flow through resistor 31'.

This results in a flow of current to the contact 54, and, since there is current flowing in the line 6, the relay 53 is in actuated or bridging po sition across the contacts 54, providing for a flow of current through the resistor or grid leak 43 to the grid 45 of the tube 26. The plate circuit of the tube 26 corresponds to the platecircuit of the tube 26 of Figure 1, and the same reference numerals have been employed to identify the same. A negative potential from the negative operating bus I6 is impressed through resistor 44' upon the grid l5n of the tube 26', and this negative potential is, counteracted by the voltage across resistor 31. 'I'he time delay for the operation of the relay 20 is controlled by a capacitor 48.', corresponding to the condenser or 5 capacitor 48 of Figure 1, provided with the selec-l tive taps 49 for eiectively controlling the chargingv rate of the condenser, and thereby eiectively controlling the rate at which the positive potential from the resistor 43 overcomes the negative potential upon the grid 45' supplied by the negative operating bus |6. y

In the embodiment shown in Figure 2 I have also provided means for indicating the deterioration in the life of the tubes I4" and 26. In the specic embodiment disclosed, the tubes |4' and 26 are provided with special plates 60 and 62, which are connected to the energizing coils 63 and 64 of relays 65 and 66. These relays, upon actuation, are adapted to bridge across contacts 20 carried by conductor 61 leading to the positive operating bus |5 and conductor 68 leading to the negative operating bus |6 to eiect actuation of an alarm means or the like shown at 69. The current for the energizing coils 63 and 64 is pro- 25 vided by separate windings of the lament transformer 30', and it is therefore apparent that the cathodes of the tubes I4' and 26 do not have to be at the same potential in order to secure this tubef-life indicating operation.

The particular operating characteristics of the tube-life indicating circuit disclosed are more clearly described in connection with my copending application,- Serial No.` 638,513, led. October 19, 1932, which is directed particularly 'to this 35 circut for indicating the ldeterioratiorrof the life of a thermionic tube, either by the lowering of the rate of electron emission from the vcathode thereof, or by the loss of vacuum withinV the tube.

Further, by providing the combination' of this 40 control means with a tube-life. indicating circuit, the loss of vacuum in the tube, or the lowering of the rate of electron emission from the cathodes of the tube can be readily ascertained, and defective tubes may be replaced before they 45 fail, thereby preventing a failu of a tube from destroying the effectiveness of the protection circuit.

Having described my invention in accordance with the patent statutes,`what I claim as new 50 and desire to secure by Letters Patent is:

1. In combination, an alternating current line, I a circuitbreaker therefor, a timing circuit including a relay adapted to actuate said circuit breaker, a thermionic tube in said circuit having a plate circuit and a grid, said plate circuit being adapted to energize said relay upon predetermined current flow therethrough, means normally maintaining said grid at a negative potential sumcient to prevent any substantial current flow through said plate circuit, means responsive to an abnormal condition on said line and including a condenser for imposing a positive potential on said grid to produce current flow in said plate circuit, and means for varying the charging rate of said condenser, and means for controlling said positive potential in accordance with the line current valve in said alternating current line.

2. In combination, a station bus, an alternating current line, a circuit breaker therebetween, means including a thermionic tube responsive to abnormal phase relationship between said bus and line for allowing plate current ow through Sid tube, an independent timing circuit for operating said breaker, means normally imposing a substantially constant negative potential on said timing circuit, means normally preventing operation of said breaker by said timing circuit, means responsive to minimum plate current flow in saidA first tube for energizing said timing cir- 4cuit including means for supplying direct current at a positive potential to said timing circuit for biasing said timing circuit to operate said breaker, and means providing for control of the rate at which said positive potential is supplied in accordance with the line current flow in said alternating current line.

3. In combination,.an alternating current line, a circuit breaker therefor, a hot cathode tube having a plate circuit adapted to trip said circuit breaker upon predetermined current flow therethrough, a grid for said tube, means normally maintaining said grid at a negative potential preventing substantial current flow through said plate circuit, relay means operable upon reversal of current iiow in said line for connecting said grid to a line current transformer, said relay means including rectifying means for imposing a counter potential upon said grid for overcoming said negative potential to permit current flow in said plate circuit, and means controlling the length of time elapsing before said counter potential is sufficient to permit said predetermined current iiow through said plate circuit, and means responsive to line current ow for controlling the value of the counter potential imposed on said grid.

4. A timing circuit for operating current interrupting means on an alternating current line including a thermionic tube having a plate circuit, means controlled by predetermined current ow through said plate circuit for actuating said interrupting means, a saturating transformer on said line, a grid for said tube,4 a direct current operating bus normally maintaining said grid at interposing a time ldelay between operation of' said rectifying means and biasing of the potential on said grid.'

5. In combination, in a three-phase alternating current system, directional power relay means therefor, a timing circuit including three thermionic tubes having plate circuits, grids for i each of said tubes, means for normally maintaining a negative potential on said grids for preventing any substantial current flow through v the plate circuits, and means responsive to actuation of said relay means for imposing a positive potential on at least one of said grids to permit predetermined current flow through the corresponding plate circuit, circuit breaker means for said three-phase system operated by said predetermined current Vflow through any oneof said relay means in said system, a thermionic timing circuit, means energized by predetermined current flow in said system for conditioning said timing circuit for operation, means including a saturating transformer in said system energized 5 upon operation of said relay means for supplying direct current to said timing circuit in accordance with the current flow in said system, means in said timing circuit controlling the rate at which said direct' current is supplied thereto, l0 and means in said timing circuit responsive to a predetermined increase in positive potential therein for actuating said circuit breaker.

7. In combination, in'an alternating current system, a timing circuit including a thermionic l5 tube, meansfor normally maintaining a negative bias on the grid of said tube to prevent current ow through said tube, means responsive to a predetermined current flow -in said system for conditioning said timing circuit for operation, a

thermionic power relay responsive to abnormal conditions in said system for imposing a positive potential direct current on said grid including a saturating current transformer in said system for supplying said potential in accordance with the current flow through said system.

8. In combination, in an alternating current system, an alternating current line, a circuit breaker in said line, trip ,means for actuating said breaker, a timing circuit including a thermionic tube, means for normally maintaining a negative bias on the grid of said tubeto prevent current flow through said tube, means actuated by current ilow through said tube for operating said trip means, means responsive to a predetermined current ilow in said system for conditioning said timing circuit for operation, a thermionic power relay responsive to abnormal conditions in sai-d system for imposing a positive potential direct current lon said grid including a saturating current transformer in said system for supplying said potential in accordance with the current'flow through said system.

9. In combination, an alternating current line,

a timing circuit including ya grid and a plate circuit, means actuated by predetermined current ow through said plate circuit for interrupting the circuit through said line, means normally maintaining a negative potential on said grid to prevent said current flow through said plate cir- 4cuit, a separate circuit for supplying a positive potential to said grid, a switch in said separate circuit, means responsive to predetermined current ow in said line for closing said switch, and a thermionic power relay responsive to abnormal conditions in said line for imposing a direct current positive potential on said separate circuit in accordance with current flow in said line to overcome said negative potential to provide for current flow through said plate circuit. 10. In combination, an alternating current line, a timing circuit including a thermionic tube, means for normally maintaining a negative potential in the grid of said tube to prevent current now therethrough, a separate circuit for the grid of said tube, a current transformer in said line and adapted to maintain said separate circuit in operating condition upon predetermined minigrid circuit to overcome said negative potential?5l aoeaese on said grid for permitting current ow through said tube.

1l. ln combination, an alternating current line, means for interrupting the circuit through said line, a timing circuit including a thermionic tube, means normally maintaining a negative potential on the grid of said tube, condenser means in the grid circuit of said tube, means normally maintaining a negative potential on said condenser means, means responsive to abnormal conditions in said line for producing a positive direct current potential, said means imposing said positive potential on said grid and condenser means quantitatively in accordance with line currentcow, and means in said timing circuit actuated by a predetermined positive potential on said grid'or energizing said interrupting means.

l2. in a three phase alternating current system, alternating current lines, a circuit breaker for said lines, trip means for actuating said breaker, 'timing circuits for each of said lines including thermionic tubes having grids, means normally maintaining a negative potential on said grids, individual plate circuits for each of said tubes individually operable when a predetermined positive potential is impressed on said grids for energizing said trip means, means energized by predetermined current ow in each of said lines for conditioning said respective timing circuits for operation, and means including. a saturating transformer for each of said lines and a thermionic power relay in the secondary circuit of each of said transformers responsive to abnormal conditions in the respective lines for imposing a direct current positive potential on said corresponding grids, said means providing for increased positive potential -on said grids in accordance with increased line current. 

